>

The yellow parts are uninhabitable desert.
The brown parts are uninhabitable due to
floods, drought or extreme weather.

If the planet warms by 4 °C – as it might by 2099 – it will change beyond all recognition, says Gaia Vince in an article in New Scientist. The article closes with the quote of Nobel prizewinning atmospheric chemist Paul Crutzen: “I would like to be optimistic that we’ll survive, but I’ve got no good reason to be. In order to be safe, we would have to reduce our carbon emissions by 70 per cent by 2015. We are currently putting in 3 per cent more each year.”

Reducing emissions by 70 per cent in six years? That will never happen. Never. Mankind is simply too dumb.
People will definitely be forced to migrate in order to survive. It will require “a wholesale relocation of the world’s population according to the geography of resources”, meaning moving people where the water is. In the northern hemisphere they’ll end up in Scandinavia, Siberia and Canada. In the southern hemisphere, “Patagonia, Tasmania and the far north of Australia, New Zealand and perhaps newly ice-free parts of the western Antarctic coast”.
Like a friend of mine just said: “Soon you’ll be begging us to let you move to Sweden”…

You might also want to read A survey of the the sea: Troubled waters, a series of nine articles in The Economist. Start with the first one, Troubled waters, and read on.
“It is clear, in any event, that man must change his ways. Humans could afford to treat the sea as an infinite resource when they were relatively few in number, capable of only rather inefficient exploitation of the vasty deep and without as yet a taste for fossil fuels. A world of 6.7 billion souls, set to become 9 billion by 2050, can no longer do so. The possibility of widespread catastrophe is simply too great.”